The basic principle of clean eating is trying to eat to the best of your ability, whole, fresh, unprocessed foods. Food that occurs in nature and do not go through extensive processing.
Preparing the food by yourself will help your chances of being successful on a clean eating plan. Going out to restaurants is not restricted but unfortunately the food served there is not as fresh and most likely processed, resulting in less nutritional value. If you are not used to cooking in the kitchen start with basics and move up from there.